Distinct 14C plateaus during glacial termination IA were employed to trace changes in the paleoreservoir age of surface and intermediate-water masses at key positions in the Icelandic Sea, far northwestern Pacific, Santa Barbara Basin, and South China Sea over an interval crucial for postglacial ocean reorganization and atmospheric pCO2 rise. Also, the plateaus provide a high-precision tool to correlate paleoceanographic signals with ice core records of climate change. Calendar year ages of the 14C plateaus were defined by means of high-resolution atmo-spheric 14C records deduced from varve, tree ring, and coral U/Th-dated series of 14C dates. A “rugged“, exceptionally broad plateau occurs at 13.3-12.8 (atmospheric) 14C ka, a smooth plateau at 12.2-12.0 14C ka, two further short plateaus at 14.0 and 11.8 14C ka. Using these plateaus for age control, surface water reservoir ages in the northern South China Sea were found to decrease from 1100 yr during H1 to 800 yr after the early Bølling and 500 yr today, suggesting a decreased admixture of upwelled “old“ deepwater. On the other hand, reservoir ages of surface water in the subarctic northwest Pacific, the terminus of global thermo-haline circulation (THC), were reduced to 350 yr during H1 and 450/500 yr from the Bølling to the Younger Dryas, as compared to 700-900 yr today and document a convection of intermediate water in this sea region during Termination 1, as corrob-orated by a coeval drop in benthic reservoir ages from 2600 to 1400 yr at 2300 mwd. In the southern Icelandic Sea, the modern source region of global THC, planktic reservoir ages reached 2300 yr during the last glacial and Termination IA (today: 400 yr), whereas benthic reservoir ages at 800 mwd were as low as 400 yr. Thus, the peak glacial overflow of deepwater continued to flow southward from the Norwegian Sea. Only the onset of H1 led to an abrupt increase in benthic reservoir ages to 1650 yr and an overflow reversal. In the Santa Barbara Basin planktic reservoir ages decreased from 1850 yr during most of H1 to 1150 yr near its end and to 750 yr during and after the Bølling (today: 630 yr). High values for H1 imply upwelling of old source water, indeed con-firmed by extreme (3700 yr) benthic reservoir ages of intermediate water (600 mwd), possibly derived from the distant Southern Ocean. After 16 cal. ka benthic ages decreased to 1750 yr in the Bølling.
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